1. Field of the Invention
The present invention relates to a method for transmitting data in a telecommunication system including at least one transmitter and one receiver, said transceiver being intended to transmit a signal formed by at least one sequence of Np pulses over Np time windows, each pulse being enclosed within a time chip whose position whithin its relevant time window is defined by a chip number.
2. Discussion of the Background
Such data transmission methods are currently studied with the aim of assessing the relevance of so-called Ultra-Wide Band telecommunication systems (further referred to as UWB systems). In such a system each transmitter may be identified by a signature formed by the above-mentioned chip numbers, which signature is in itself quite sturdy and may thus be reliably and accurately communicated to all potential receivers.
The pulses used in UWB systems are very short, having for example a duration lower than 0.1 nanosecond, which offers to such systems bandwidths at least as large as 10 GigaHertz, entailing high flexibility and hence numerous possible applications for such systems.
The above-described signal may form a carrying signal on which information can be encoded by modulation of said carrying signal, for example by performing phase or amplitude modulation of one or more pulse sequences.
In currently used telecommunication systems, a transmitter of data usually inserts a header to be transmitted before transmitting the actual information contained in the modulated signal. This header includes pulse sequences describing predetermined reference symbols, which are known beforehand by the receiver, so that said receiver may judge, by analyzing received symbols representative of said reference symbols, how communication conditions between the transmitter and the receiver actually affect the transmitted data. This analyzis of the received reference symbols enables the receiver to adjust a processing to which further pulse sequences carrying said actual information will be subjected to by the receiver.
The receiver must thus be able to identify the received reference symbols, and, to this end, be able to precisely identify the beginning of a pulse sequence carrying such a reference symbol. Such an identification of the beginning of a sequence is often referred to as a detection and synchronization step by those skilled in the art.
In the present state of the art, signal detection and synchronization is often performed by correlating a received signal delivered at the output of a receiving antenna, which received signal may be exclusively constituted by noise or, alternatively, may include an incoming carrying signal, with a gliding model of the waveform such a carrying signal should have.
Though such a gliding correlation technique enables to map a whole pulse sequence and thus allows a detection and an identification of the beginning of the sequence, this technique is not realistically applicable as such to the detection of sequences of Np pulses lasting less than 0.1 ns each and enclosed in time windows having each a width of roughly 100 ns. In such an example, with for example Np=128 and a sampling interval of 10 ps, the scanning of the whole duration of a pulse sequence would require 1,28.106 successive pulse sequences for its completion and would then last 16 seconds, which is not acceptable.
It should be also be noted that, during the considerable time required for performing the mapping of a pulse sequence according to the gliding correlation technique described above, communication conditions between the transmitter and the receiver may change, i.e. a communication channel between these devices may be altered, for example due to movements of one or both devices, so that the communication conditions may be altered in the course of a single signal detection and synchronization step, with adverse effects on the accuracy of the results yielded by said signal detection and synchronization step. The signal carrying the pulse sequences may even disappear before its very detection is completed.